Tungsten halogen automotive lamps having a bluish coating to shift the color temperature of the light produced to a whiter, higher color temperature are known, such as in U.S. Pat. No. 6,369,510 (Shaw). A commercial embodiment of a lamp depicted in the Shaw Pat. '510 is sold in the United States by Osram Sylvania Inc. (OSI) under the trade designation “Silverstar” in which the capsule's entire light-emitting region (disregarding the upper dome, which is opaque, for glare control) has a bluish coating. The bluish coating is an absorption coating on the glass outer envelope that absorbs light at a peak of around 600 nm (the yellow-red region), and although the transmission of the bulb still results in a continuous output spectrum, it has a lower “yellow” content than uncoated halogen sources, see FIG. 6 of Shaw Pat. '510. Because the entire capsule is coated, the entire beam distribution has a color temperature of about 3800° K (in comparison, an uncoated, standard 9006-type halogen capsule produces that beam distribution with a lower color temperature of about 3050° K).
A whiter beam color is perceived stylistically as aesthetically pleasing and can approximate the appearance of more expensive HID (High Intensity Discharge) lamps. The higher color temperature beam has the functional advantage of improved color contrast to aid obstacle detection and road surface orientation. The higher color temperature beam has the further functional advantage of higher effective intensity in peripheral vision, where the retina of the eye has proportionately more photoreceptors of the type that are rods than the type that are cones. Rods are more sensitive to blue light than the cones which are in the retina's central fovea region and are predominantly found in central vision, as discussed in Derlofske et al., “Visual Benefits of Blue Coated Lamps for Automotive Forward Lighting” (Society of Auto. Engineers 2003-01-0930). Higher color temperature light could, in theory, have an advantage in maintaining operator alertness at night. However, there is a tradeoff in that it is understood that while whiter light does not cause an increase in disability glare, there is an increase in perceived discomfort glare, as discussed in Sivak et al., “LED Headlamps: glare and color rendering”, Lighting Res. The. 36,4 (2004) at pp. 295-305.
Also known is PCT WO 2008/074657 (Leunnemann). A tinted vehicle lamp similar to that depicted in FIG. 2 of the PCT WO 2008/074657 has been marketed by Osram Sylvania Inc. in the United States under the trade designation “Night Breaker”. This lamp also uses a coating of the type in Shaw Pat. '510 which absorbs more yellow, red and green wavelength light than it does blue and violet light. The “Night Breaker” lamp is shown herein at FIGS. 1 and 2. The uncoated part of the lamp illuminates the hot spot part of the optics in the headlight, producing yellower light for the hot spot without intensity loss from having passed through the coating. A portion of the spread optics is illuminated by light which has first passed through the blue coated part of the lamp. However, there is still a large proportion of spread optics beam which receives light which does not pass through the blue coating.
As shown in FIG. 1, the “Night Breaker” lamp capsule with axial filament has a non-light transmissive dome 50, for example black paint, at its top and the two coated bluish regions are indicated in cross-hatching. There is an uninterrupted, uncoated band-like region that separates the two coated regions, the uncoated region extending around the entire capsule. The capsule diameter is 12.06 mm, and the uncoated circumferential band is 5.5 mm+/−1 as measured along the axial direction. The uncoated band, of nominal height 5.5 mm, is centered on the light center length (LCL) of the filament. A coating can be provided on the press seal 40 for manufacturing convenience but that is not optically relevant since the press seal becomes held inside the base connector coupling it to the reflector. As shown in FIG. 2, the spacing of the upper edge of the lower region of coating from the filament is such that light emitted from the capsule in a direction toward the capsule base passes through the uncoated widow along a conical envelope directed toward the capsule base and subtended by an angle, referred to as an extent angle, of about 130 to 137 degrees centered on the filament. Similarly, light extends along a similar conical envelope directed forward (direction of dome 50), but that is not light that is managed by the reflector.
The following lamps are also known: U.S. Pat. No. 6,093,999 (English); U.S. Pat. No. 6,281,630 (English); U.S. Pat. No. 6,342,762 (Young); U.S. Pat. No. 7,362,049 (Raukas); U.S. Pat. No. 6,731,051 (Oetken); U.S. Pat. No. 6,670,768 (Labant); U.S. Pat. No. 7,670,037 (Devir); U.S. Pat. No. 6,60,462 (Bockley); U.S. Pat. No. 7,178,957 (Schug); U.S. Pat. No. 5,017,825 (Heijnen); and U.S. Pat. No. 6,508,573 (Yamazaki).
For a thorough understanding of the present disclosure, reference is made to the following detailed description, including the appended claims, in connection with the above-described drawings. Although the present disclosure is described in connection with exemplary embodiments, the disclosure is not intended to be limited to the specific forms set forth herein. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient. Also, it should be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.